1. Field of the Invention
The present invention relates to a solid-state imaging device. More particularly, the present invention relates to a solid-state imaging device in which a plurality of light-sensitive elements are arranged in a matrix form.
2. Description of the Background Art
In order to improve the light collecting power of a solid-state imaging device typified by a CCD, there exists a solid-state imaging device in which two micro lenses are formed as shown in FIG. 8. Hereinafter, with reference to FIG. 8, the above-described solid-state imaging device will be described.
The solid-state imaging device as shown in FIG. 8 includes a semiconductor substrate 501, a gate insulating film 502, a gate electrode 503, a photodiode 504, a charge transfer section 505, an interlayer insulating film 507, a light-shielding film 508, an insulating film 509, an intralayer lens 510, a planarization film 511, a color filter 513, and an on-chip micro lens 514.
The photodiode 504 and the charge transfer section 505 are formed on the semiconductor substrate 501. A surface of the semiconductor substrate 501 is coated with the gate insulating film 502, and the gate electrode 503 is formed on the gate insulating film 502. The interlayer insulating film 507 is formed on the gate electrode 503. Further, the light-shielding film 508 is formed so as to coat the gate insulating film 502 and the interlayer insulating film 507.
Also, the insulting film 509 is formed on the light-shielding film 508. The intralayer lens 510 and the planarization film 511 are formed on the insulating film 509. Further, the color filter 513 is formed on the planarization film 511. The on-chip micro lens 514 is formed on the color filter 513 for each photodiode 504.
As described above, in the solid-state imaging device as shown in FIG. 8, the on-chip micro lens 514 is formed on the top layer of the solid-state imaging device, and the intralayer lens 510 is formed in the planarization film 511. As such, two micro lenses are formed for each photodiode 504, whereby it is possible to further efficiently collect light onto the photodiode 504.
However, the solid-state imaging device as shown in FIG. 8 has a problem that light entering the solid-state imaging device obliquely from above (hereinafter, referred to as oblique light) enters an adjacent pixel, whereby color mixing occurs.
Thus, a solid-state imaging device as shown in FIG. 9 has been developed as a solid-state imaging device capable of preventing color mixing caused by the oblique light. FIG. 9 is a cross section view of the above-described solid-state imaging device.
The solid-state imaging device as shown in FIG. 9 differs from the solid-state imaging device as shown in FIG. 8 in that reflecting walls 512a and 512b are additionally provided on both sides of the intralayer lens 510. As such, the reflecting walls 512a and 512b are additionally provided, whereby the oblique light is reflected by the reflecting walls 512a and 512b, as shown in FIG. 9. As a result, the oblique light enters the photodiode 504. Thus, it is possible to solve the problem of color mixing of the solid-state imaging device. Further, the oblique light, which is not originally collected, enters the photodiode 504, thereby improving the light sensitivity of each pixel of the solid-state imaging device (see Japanese Laid-Open Patent Publication No. 2001-77339).
In the solid-state imaging device shown in FIG. 9, the light sensitivity of the solid-state imaging device is improved as a whole. However, there is still variation in the light sensitivity among the pixels of the solid-state imaging device. Hereinafter, with reference to the drawing, such variation in the light sensitivity will be described in detail. FIG. 10 is a graph showing a distribution of light sensitivity of a camera device with an optical lens, into which a solid-state imaging device is built. Note that a vertical axis represents light sensitivity, and a horizontal axis represents a position of a pixel in the solid-state imaging device.
First, there is a certain relationship between a position of a pixel in the solid-state imaging device and an angle of incident light. Specifically, in a pixel lying near the center of the solid-state imaging device, a percentage of light incident from immediately above (light denoted as α in FIG. 9) is higher than a percentage of light having another incident angle. On the other hand, in a pixel lying in a right area of the solid-state imaging device, a percentage of oblique light incident from the left (light denoted as β in FIG. 9) is higher than a percentage of light having another incident angle. Also, in a pixel lying in a left area of the solid-state imaging device, a percentage of oblique light incident from the right (light denoted as γ in FIG. 9) is higher than a percentage of light having another incident angle.
The light incident from immediately above onto the solid-state imaging device is collected by the on-chip micro lens 514 and the intralayer lens 510, and enters the photodiode 504 with a high degree of efficiency. On the other hand, even if the oblique light is reflected by the reflecting wall 512, a portion of the oblique light is prevented from entering the photodiode 504 by the light-shielding film 508, for example. That is, the probability that the oblique light enters the photodiode 504 is lower than the probability that the light incident from immediately above enters the photodiode 504. As a result, the pixel in the right and left area with a higher percentage of oblique light has lower light sensitivity than the pixel in the central area with a lower percentage of oblique light. Specifically, as shown in FIG. 10, pixels located at the right and left edges of the solid-state imaging device have lower light sensitivity, and a pixel located at the center of the solid-state imaging device has higher light sensitivity.